The U.S. atomic monopoly was not long-lasting; the Soviet Union successfully exploded its first atomic bomb in 1949, followed later by the United Kingdom in 1952, France in 1960, and the People’s Republic of China in 1964. This directly places the end of the U.S. monopoly in 1949.

In 1949, the Soviet Union tested its first atomic bomb. The article explains that the United States had been implementing postwar policy in the context of a nuclear monopoly, and that monopoly no longer existed once the Soviet test occurred.

The Soviets embedded spies in the United States to steal military secrets, including information that helped the USSR build and test its own nuclear bomb in 1949, only four years after the Trinity test. This supports the chronology that the U.S. remained the sole nuclear power until 1949.

On 6 and 9 August 1945, the United States detonated two atomic bombs over Japan. The article states that the American monopoly on nuclear weapons lasted four years before the Soviet Union detonated an atomic bomb in 1949, indicating exclusive U.S. possession from 1945 until that year.

The United States conducted its first nuclear test explosion in July 1945 and dropped two atomic bombs on the cities of Hiroshima and Nagasaki, Japan, in August 1945. Just four years later, the Soviet Union conducted its first nuclear test explosion. The United Kingdom (1952), France (1960), and China (1964) followed.

The United States sets up the Manhattan Project to develop the first nuclear weapon. 16 July 1945 – US conducts first ever nuclear test – Trinity. 29 August 1949 – Soviet Union tests its first nuclear bomb. The Soviet Union explodes a nuclear weapon code-named “First Lightning” in Semipalatinsk, Kazakhstan, becoming the second country to develop and successfully test a nuclear device.

Following the atomic bombings of Hiroshima and Nagasaki, the Soviet Union accelerated its atomic bomb project, resulting in the RDS-1 test in 1949. … The People’s Republic of China became the fifth nuclear power on October 16, 1964, when it detonated a 25 kiloton uranium-235 bomb in a test codenamed 596 at Lop Nur.

After a successful test of the weapon, Truman issued the Potsdam Declaration. The page documents that the United States had the atomic bomb in August 1945, establishing the starting point for the monopoly period before the Soviet test in 1949.

The world's first nuclear weapons explosion [Trinity] on July 16, 1945, in New Mexico, when the United States tested its first nuclear bomb. On August 6, 1945, the United States dropped an atomic bomb on the Japanese city of Hiroshima. In subsequent years, the United States, the Soviet Union and Great Britain conducted several nuclear weapons tests. France exploded its first nuclear device in 1960 and China entered the "nuclear arms club" in October 1964 when it conducted its first test.

Nine countries. Thousands of warheads. One enduring question: Who gets to have nuclear weapons—and why? Let’s start with the original nuclear club: the US, Russia, UK, France, and China—officially recognized under the Nuclear Non-Proliferation Treaty (NPT). United States built the world's first nuclear bombs in World War II under the Manhattan Project. In 1945, the US dropped two on Japan. So the USSR sped up its own secret program and tested its first bomb in 1949 with help from spies inside the US program.

The United States became the world's first nuclear power on July 16, 1945, when it successfully detonated an atomic bomb at a testing site in New Mexico. In the following years, the Soviet Union (1949), the United Kingdom (1952), France (1960), and China (1964) developed their own nuclear weapons, followed later by other countries.

On July 16, U.S. military researchers conduct the world’s first atomic weapons test in Los Alamos, New Mexico, a culmination of the top-secret Manhattan Project. In early August, American warplanes drop atomic bombs on Hiroshima and Nagasaki, killing more than one hundred thousand Japanese people. The Soviet Union explodes its first nuclear weapon at a test range in Kazakhstan on August 29, 1949. Most U.S. intelligence assessments at the time had estimated that Moscow was at least three years away from obtaining such technology.

Nine countries currently have nuclear weapons: Russia, the United States, China, France, the United Kingdom, Pakistan, India, Israel, and North Korea. Only one country that had them — South Africa — entirely dismantled its arsenal. Historical data in the article show the United States as the first nuclear-armed state in 1945 and the Soviet Union joining in 1949, with the United Kingdom, France, and China following later in the 1950s and 1960s.

The concept of the "US nuclear monopoly" refers to the period immediately after World War II when the United States was the only country possessing nuclear weapons. This monopoly lasted until 1949, when the Soviet Union successfully tested its first atomic bomb, ending U.S. exclusivity and triggering a full-scale nuclear arms race.

American policy makers initially believed that the United States would enjoy an enduring atomic monopoly that would be decisive in dealing with Russia. Between 1945 and 1949, U.S. nuclear weapons policy was shaped by assumptions about the durability and utility of this monopoly, until the Soviet atomic test in August 1949 abruptly ended it.

In 1949, the Soviet Union tested its first atomic bomb. The article also describes the United States as clinging to its atomic monopoly that year, which frames the monopoly as ending in 1949 rather than earlier.

To date, nine countries have developed nuclear weapons: The five recognized by the NPT: United States, Russia, United Kingdom, France, China. These countries are recognized as nuclear weapon states because they tested nuclear devices before 1 January 1967, with the United States first in 1945 and the Soviet Union in 1949.

Between 1945 and 1949 the USA was the only country with nuclear weapons. Could they have conquered the world if they had chosen to? The United States possessed only a handful of nuclear weapons by 1949—exact numbers are unclear, but there were about 50 in 1948.

From 1945 until the CCCP developed its own nuclear capability (in August 1949) the USA bluffed that it had huge stockpiles of nukes (it “only” had about 50 operational weapons). When the US had that monopoly on atomic weapons, it was only atomic bombs that were impractical to deliver against an enemy with a functional Air Force, and it took a long while to get mass production going. Because at the end of WWII they did not possess any. The US had exactly two nukes and used both on Japan so they had nothing to leverage with.

In an extraordinary display of scientific and industrial might, the United States made two bombs ready for use by August 1945. Germany was defeated by then, but Japan was not, and so the bombs were used on Hiroshima and Nagasaki. At that time no other country had operational nuclear weapons, and the U.S. briefly possessed a unique capability that shaped early Cold War dynamics until the Soviet test in 1949.

In Nuclear Monopoly George Quester sets forth the case for preventive war using rudimentary atomic weapons to avoid the possibility of a future war in which nations engage in unrestricted nuclear warfare. He analyzes historical episodes when one state briefly possessed nuclear weapons while others did not, focusing particularly on the American monopoly from 1945 to 1949 and the strategic debates it provoked.

This study examines how nuclear weapons affected the escalation of the Cold War from 1945 to 1962, including the period when the United States was the sole possessor of atomic weapons. The early years after Hiroshima and Nagasaki were characterized by U.S. nuclear monopoly, which ended with the Soviet Union’s successful test in 1949, fundamentally transforming the strategic environment.